Exemplary embodiments of the invention relate to a longitudinally adjustable steering column for a motor vehicle, in particular a passenger motor vehicle.
German patent document DE 10 2010 051 880 A1 discloses a longitudinally adjustable steering column in which an inner jacket pipe of the steering column, which receives a steering spindle, is received in a longitudinally adjustable manner in an outer jacket pipe, which for its part is held in a height-adjustable manner on a steering console fastened on a shell side of the motor vehicle. The steering column furthermore comprises a clamping device, by means of which the inner jacket pipe can be secured releasably in its adjusted longitudinal position relative to the outer jacket pipe.
In order to guarantee a comfortable adjustment in such mechanically adjustable steering columns the adjustment force that is to be applied manually must be as low as possible in the released state of the clamping device, i.e., when the inner jacket pipe is released in its movement relative to the outer jacket pipe. On the other hand when the clamping device is in the locked state it is necessary for the required sliding seat between the inner and the outer jacket pipe to be as rigid as possible for a high level of rigidity or resonant frequency of the steering column. There thus arises a technical conflict between an adjustment of the inner to the outer jacket pipe, which is as smooth as possible, for a released clamping device on the one hand, and a securing of the inner jacket pipe relative to the outer jacket pipe, which is as rigid as possible, for a locked clamping device.
This problem is further intensified by the requirement that the steering column be designed with both jacket pipes for the absorption of impact energy caused by an accident, and also that only a limited amount of space be available. Especially in this case, hitherto existing solutions in which, for example, plastic injection is provided between both jacket pipes for tolerance compensation, which is disclosed, for example, in German patent document DE 103 43 685 A1, are not suitable.
Finally, German patent document DE 197 07 067 C1 discloses a steering column unit for a motor vehicle in which a jacket pipe is used that has a groove slot. This groove slot prevents torsion, such that the jacket pipe can be fixed with positional accuracy at a fastening point on sides of a steering console.
Exemplary embodiments of the present invention are directed to an adjustable steering column in which the inner jacket pipe is smoothly longitudinally adjustable relative to the outer jacket pipe and can be rigidly secured.
In order to create a steering column of the type cited at the start with an inner jacket pipe, which on the one hand can be adjusted smoothly for longitudinal adjustment relative to the outer jacket pipe, and which on the other hand can be secured particularly rigidly to the outer jacket part to guarantee a high level of rigidity or resonant frequency of the steering column, according to the invention the outer jacket pipe has at least one recess above a longitudinal region, whereby its hollow cross-section can be altered by means of the clamping device. In other words, according to the invention the hollow cross-section of the outer jacket pipe, at least over a partial length, includes a recess, for example in the form of a longitudinal slot, such that its hollow cross-section can be enlarged or reduced in a simple manner by means of the clamping device, according to whether the inner jacket pipe is to have its length adjusted or is to be fixed.
By providing such a recess, a correspondingly widened hollow cross-section of the outer jacket pipe can thus on the one hand be achieved—in the case of a released clamping device—such that the inner jacket pipe can be smoothly axially displaced relative to the outer jacket pipe. On the other hand, the hollow cross-section can be reduced in size in a simple manner by means of the clamping device in such a way that as reliable and fixed a securing as possible of the inner jacket pipe arises in its adjusted longitudinal position relative to the outer jacket pipe. Thus, overall, a steering column with high rigidity and resonant frequency can be obtained.
A further advantageous embodiment provides that the recess is formed to be open towards a steering wheel side of the outer jacket pipe. With such a recess of the outer jacket pipe, its hollow cross-section can be varied in diameter in a particularly simple manner by means of the clamping device, such that a particularly expedient longitudinal adjustment can be achieved and as rigid a securing as possible of the inner jacket pipe relative to the outer jacket pipe can be achieved.
Here, it has been shown to be advantageous in a further embodiment of the invention if the recess is at least substantially formed as a slot running in the axial direction of the outer jacket pipe. Such a slot can be produced particularly simply in terms of manufacturing technology.
Is it furthermore advantageous for the clamping device to comprise a clamping wedge device. Such a clamping wedge device enables a particularly reliable securing of the inner jacket pipe relative to the outer jacket pipe, in particular if the steering column is to be able to be used for the absorption of impact energy.
In a further advantageous embodiment a force element, in particular a clamping plate, is provided between a clamping element of the clamping device and the outer jacket pipe. The advantage of such a clamping plate or such a force transmission element is that this can have, in a simple manner, an enlarged clamping face, such that, during clamping, corresponding clamping forces can be transferred to the outer jacket pipe.
Here, it has been shown to be advantageous in a further embodiment of the invention if the force transmission element is coupled for movement with the inner jacket pipe via a driver connection pushing through the outer jacket pipe. With this driver connection, the force transmission element, in particular the clamping plate, is picked up by the inner jacket pipe if the inner jacket pipe is adjusted relative to the outer jacket pipe or, in the case of an application of force caused by an accident, the inner jacket pipe is pushed in a telescopic manner into the outer jacket pipe. Here, the driver connection is preferably designed to be positive and/or firmly bonded, since a particularly reliable connection between the force transmission element and the inner jacket pipe is to be hereby achieved.
In a further advantageous embodiment a longitudinal hole is hollowed out of the outer jacket pipe for the driver connection. Here, this longitudinal hole can, for example, be designed in such a way that it serves as a guide for the driver connection.
In a further advantageous embodiment, at least one friction-increasing element is allocated to the clamping device. This can be a corresponding friction film, which, for example, is arranged between a clamping element of the clamping device and the outer jacket pipe or the force transmission element. Alternatively, a coating or suchlike would also be conceivable. On the one hand, a particularly secure fixing of the inner jacket pipe relative to the outer jacket pipe can hereby be achieved and, on the other hand, the accident force, which may potentially be absorbed by the steering column, is increased.
Finally, it has been shown to be advantageous if the outer jacket pipe is held on the steering console in a height-adjustable manner. There hereby arises a steering column that can be adjusted in all major directions having the advantages described above.